Wet ground calcium carbonate as well as preparation method and application thereof

Abstract

The invention provides wet ground calcium carbonate as well as a preparation method and application thereof, and belongs to the technical field of fine chemical engineering. Marble particles are ground and then mixed with water, obtained marble slurry is mixed with a first grinding aid, the first grinding aid comprises a nonionic fatty alcohol ethyoxyl compound and polyethylene glycol, first wet grinding is carried out, the obtained first slurry is mixed with a second grinding aid, second wet grinding is carried out, and the marble slurry is obtained. The second grinding aid comprises a high-molecular block copolymer containing a pigment-friendly filler group and an alkynediol ethylene oxide adduct, and carrying out wet classification and flash drying on the obtained second slurry to obtain wet ground calcium carbonate. According to the invention, a two-section series wet-process stirring process is adopted, the phenomenon of material agglomeration in the drying process of a traditional wet-process grinding process is effectively avoided by adjusting the solid content of the marble slurry, screening a grinding aid and selecting a wet-process grading process, and the defect that the particle size of the existing finished product heavy calcium carbonate is obviously larger than that of the material in the slurry is overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of fine chemical engineering, and particularly relates to a wet-process heavy calcium carbonate, a preparation method thereof, and an application thereof. Background Art

[0002] Heavy calcium carbonate has the remarkable advantages of high chemical purity, large inertness, not easy to have chemical reactions, good thermal stability, not decomposing below 400 °C, high whiteness, low oil absorption rate, low refractive index, soft texture, dryness, no crystal water, low hardness, small abrasion value, non-toxic, odorless, tasteless, and good dispersibility. Therefore, it is widely used in the fields of coatings, plastics, rubber, and papermaking.

[0003] At present, the processing technologies of heavy calcium carbonate mainly include two types: dry method and wet method. Among them, the dry production process is widely used to produce heavy calcium carbonate products with a particle size of more than 5 μm due to its short process flow and no emissions. 97 For the wet method, the powder is configured into a slurry, and zirconia beads or ceramic beads are used as the grinding medium for wet grinding. Subsequently, the slurry is dried by spray or flash evaporation to obtain the finished product. Generally, it is suitable for producing ultra-fine heavy calcium carbonate with a particle size of less than 5 μm. However, in the traditional wet grinding process, in order to increase the solid content and grinding efficiency, various ionic grinding aids are often added. During the subsequent drying process, due to the competitive adsorption of the ionic grinding aids, particle agglomeration is likely to occur, resulting in the defect that the particle size of the finished heavy calcium carbonate is significantly coarser than that of the materials in the slurry, and the performance improvements such as thixotropy, covering power, and storage stability brought by the ultra-fine mineral filler when applied to downstream coatings cannot be fully exerted. 97 Therefore, how to effectively avoid the agglomeration of heavy calcium carbonate powder during the wet grinding process due to drying, so that the functional role of the ultra-fine powder cannot be fully exerted, has become an urgent problem to be solved in the industry.

[0004] Summary of the Invention The purpose of the present invention is to provide a wet-process heavy calcium carbonate, a preparation method thereof, and an application thereof, so as to avoid the particle agglomeration problem caused by drying in the traditional wet grinding process, and when it is applied to coatings, the performance improvements such as thixotropy, covering power, and storage stability brought by the ultra-fine calcium carbonate can be fully exerted.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a wet-process heavy calcium carbonate, comprising the following steps:

[0007] Grind marble particles, and mix the obtained coarse marble powder with water to obtain a marble slurry;

[0008] ​

[0009] Mix the marble slurry with a first grinding aid and conduct first wet grinding to obtain a first slurry;

[0010] Mix the first slurry with a second grinding aid and conduct second wet grinding to obtain a second slurry;

[0011] Conduct wet classification on the second slurry to obtain a classified slurry;

[0012] Conduct flash drying on the classified slurry to obtain wet ground calcium carbonate;

[0013] The first grinding aid includes a non-ionic fatty alcohol ethoxylate and polyethylene glycol;

[0014] The second grinding aid includes a polymer-type block copolymer containing a pigment-affinity filler group and an alkynediol ethylene oxide adduct.

[0015] Preferably, the marble particles are obtained by cleaning and coarse crushing of marble ore with a calcium carbonate content of ≥90 wt%, and the diameter of the marble particles is 10 - 50 nm.

[0016] Preferably, the particle size of the marble coarse powder is 325 - 400 mesh; the solid content of the marble slurry is 40 - 50 wt%.

[0017] Preferably, the mass of the first grinding aid is 0.5 - 1‰ of the mass of the marble coarse powder, and the time of the first wet grinding is 30 - 40 min;

[0018] The first wet grinding is carried out in a first vertical stirred mill. The first grinding aid is divided into a first part of the first grinding aid and a second part of the first grinding aid. The first part of the first grinding aid is mixed with the marble slurry, and the second part of the first grinding aid is added through the top of the first vertical stirred mill;

[0019] The D 50 of the material in the first slurry is 1.5 - 1.7 μm, D 97 is 3.2 - 3.4 μm, and the mass ratio of the material with a particle size ≤2 μm in the first slurry > 65%.

[0020] Preferably, the mass of the second grinding aid is 0.5 - 1‰ of the mass of the marble coarse powder, and the time of the second wet grinding is 30 - 40 min;

[0021] The second wet grinding is carried out in a second vertical stirred mill. The second grinding aid is divided into a first part of the second grinding aid and a second part of the second grinding aid. The first part of the second grinding aid is mixed with the first slurry, and the second part of the first grinding aid is added through the top of the second vertical stirred mill.

[0022] Preferably, the D of the material in the classified slurry 50 = 0.6 - 0.7 μm, D 97 = 1.2 - 1.3 μm, D 100 = 1.5 - 1.6 μm.

[0023] Preferably, the heat source for the flash drying is natural gas. During the flash drying, the heat source temperature is 380 - 400 °C, the outlet temperature is 200 - 220 °C, and the current of the blower is 180 - 190 A.

[0024] Preferably, the non-ionic fatty alcohol ethoxylate compound includes LμmitenN-OC 30, the average molecular weight of the polyethylene glycol is 1000, and the mass ratio of the non-ionic fatty alcohol ethoxylate compound to the polyethylene glycol is 1:2 - 4;

[0025] The high molecular type block copolymer containing a pigment filler group includes SN-1798, the alkynediol ethylene oxide adduct includes SN-3740, and the mass ratio of the high molecular type block copolymer containing a pigment filler group to the alkynediol ethylene oxide adduct is 3 - 5:1.

[0026] The present invention provides the wet-ground heavy calcium carbonate prepared by the above preparation method. The D of the wet-ground heavy calcium carbonate 50 = 0.6 - 0.7 μm, D 97 = 1.2 - 1.3 μm, D 100 = 1.5 - 1.6 μm.

[0027] The present invention provides the application of the above wet-ground heavy calcium carbonate in the coating field.

[0028] Advantages of the present invention:

[0029] In the first wet grinding of the present invention, a non-ionic fatty alcohol ethoxylate compound and polyethylene glycol with an average molecular weight of 1000 are compounded as the first grinding aid. By utilizing the excellent rapid dispersion and good fluidity of the low molecular weight dispersant, the grinding efficiency is improved; in the second wet grinding, a high molecular type block copolymer containing a pigment filler group and an alkynediol ethylene oxide adduct are compounded as the second grinding aid. By utilizing the excellent steric hindrance effect of the high molecular type super dispersant and the extremely low dynamic surface tension of the alkynol ethylene oxide adduct, the grinding efficiency is effectively improved. At the same time, the defect of particle aggregation caused by the possible competitive adsorption of the ionic dispersant during the drying process is avoided. Through the reasonable combination of the grinding aids in the two-stage wet grinding, the original particle size of the marble coarse powder material in the slurry state is maintained.

[0030] The present invention adopts a two-stage series wet stirring and grinding process. By adjusting the solid content of the marble slurry, screening grinding aids, and selecting the wet classification process, an ultra-fine wet ground calcium carbonate is prepared, effectively avoiding the phenomenon of material agglomeration easily caused during the drying process in the traditional wet grinding process, and overcoming the defect that the particle size of the existing finished product of ground calcium carbonate coarse powder is significantly coarser than that of the material particles in the slurry. As detected by a Malvern 3000-E laser particle size analyzer, the D 50 of the slurry of the wet ground calcium carbonate prepared in the present invention and the marble coarse powder is 0.6 - 0.7 μm, the D 97 is 1.2 - 1.3 μm, and the D 100 is 1.5 - 1.6 μm. Description of the Drawings

[0031] Figure 1 It is a process flow diagram for preparing wet ground calcium carbonate in Example 1. Detailed Embodiments

[0032] The present invention provides a method for preparing wet ground calcium carbonate, which includes the following steps:

[0033] Grind marble particles, and mix the obtained marble coarse powder with water to obtain a marble slurry;

[0034] Mix the marble slurry with a first grinding aid and conduct first-stage wet grinding to obtain a first slurry;

[0035] Mix the first slurry with a second grinding aid and conduct second-stage wet grinding to obtain a second slurry;

[0036] Conduct wet classification on the second slurry to obtain a classified slurry;

[0037] Conduct flash drying on the classified slurry to obtain wet ground calcium carbonate;

[0038] The first grinding aid includes non-ionic fatty alcohol ethoxylate and polyethylene glycol;

[0039] The second grinding aid includes a high-molecular type block copolymer containing a pigment-affinity filler group and an alkynediol ethylene oxide adduct.

[0040] In the present invention, unless otherwise specified, the raw materials required for preparation are all commercially available products well-known to those skilled in the art.

[0041] The present invention preferably conveys marble particles into a ring-roll mill (model YFM-208) through a spiral auger for grinding to obtain marble coarse powder; mix the marble coarse powder with water to prepare a marble slurry.

[0042] In the present invention, the marble particles are preferably obtained by washing, air-drying, jaw crushing, and hammer crushing of marble ore with a calcium carbonate content of ≥90 wt%, and the diameter of the marble particles is preferably 10 - 50 nm.

[0043] In the present invention, the particle size of the marble coarse powder is preferably 325 - 400 mesh.

[0044] In the present invention, the solid content of the marble slurry is preferably 40 - 50 wt%, and more preferably 45 - 50 wt%. In the traditional wet process for grinding calcium carbonate, a large amount of ionic dispersant is added to reduce viscosity, and the solid content of the slurry is generally above 65%. However, the addition of a large amount of ionic dispersant leads to agglomeration of the material during the subsequent drying process. In the present invention, to avoid subsequent agglomeration problems, the use of ionic dispersant as a grinding aid is abandoned. Therefore, the viscosity of the slurry is higher than that of the traditional wet process, so a relatively low solid content is controlled for wet grinding.

[0045] In the present invention, the marble slurry is preferably mixed with a first grinding aid and subjected to first wet grinding to obtain a first slurry.

[0046] In the present invention, the first grinding aid preferably includes non-ionic fatty alcohol ethoxylate and polyethylene glycol. The non-ionic fatty alcohol ethoxylate preferably includes LμmitenN-OC 30 (purchased from BASF), and the average molecular weight of the polyethylene glycol is preferably 1000, denoted as PEG-1000 (purchased from Nantong Yixun Biotechnology Co., Ltd.);

[0047] The mass ratio of the non-ionic fatty alcohol ethoxylate LμmitenN-OC 30 to polyethylene glycol is preferably 1:2 - 4, and more preferably 1:3 - 4; the excellent rapid dispersion and good fluidity of the low molecular weight dispersant are utilized to improve the grinding efficiency.

[0048] In the present invention, the mass of the first grinding aid is preferably 0.5 - 1‰ of the mass of the marble coarse powder, and more preferably 0.8 - 1‰.

[0049] In the present invention, the first wet grinding is preferably carried out in a first vertical stirring mill. The specification of the first vertical stirring mill is preferably 3600L, and the grinding medium is preferably zirconia beads with a specific gravity of 6.0 g / cm 3 ³. The filling rate of the zirconia beads in the first vertical stirring mill is preferably 60 - 70%, and the size of the grinding medium preferably includes 1.0 mm and 1.8 mm. The mass ratio of the 1.0 mm and 1.8 mm zirconia beads is preferably 2 - 4:1, and more preferably 3 - 4:1.

[0050] In the present invention, the first grinding aid is preferably divided into a first part of the first grinding aid and a second part of the first grinding aid. The mixing of the marble slurry with the first grinding aid preferably includes stirring the marble slurry for 5 - 10 minutes and then mixing it with the first part of the first grinding aid, followed by a first stirring. The obtained first stirred slurry is preferably pumped into a first vertical stirring mill, and the second part of the first grinding aid is preferably added through the top of the first vertical stirring mill. In the present invention, the first grinding aid is added in two portions to make more full use of the dispersant. There is no ratio limit for the quality of the first grinding aid added in two times in the present invention. In the examples, the mass ratio of the first part of the first grinding aid to the second part of the first grinding aid is preferably 1:1.

[0051] In the present invention, the time of the first stirring is preferably 10 minutes; the time of the first wet grinding is preferably 30 - 40 minutes, more preferably 35 - 40 minutes.

[0052] In the present invention, the D of the materials in the first slurry 50 is preferably 1.5 - 1.7 μm, more preferably 1.55 - 1.67 μm, and even more preferably 1.62 μm; the D 97 is preferably 3.2 - 3.4 μm, more preferably 3.26 - 3.37 μm, and even more preferably 3.31 μm; the mass proportion of the materials with particle size ≤ 2 μm in the first slurry is preferably > 65%, more preferably 66.2%, 68.5% or 70.6%.

[0053] In the present invention, the first slurry is preferably mixed with a second grinding aid for a second wet grinding to obtain a second slurry.

[0054] In the present invention, the second grinding aid preferably includes a polymer - type block copolymer containing a pigment - wetting filler group and an alkynediol ethylene oxide adduct. The polymer - type block copolymer containing a pigment - wetting filler group preferably includes SN - 1798 (purchased from Shanghai Shenzhu Chemical Technology Co., Ltd.), and the alkynediol ethylene oxide adduct preferably includes SN - 3740 (purchased from Shanghai Shenzhu Chemical Technology Co., Ltd.);

[0055] The mass ratio of the polymer - type block copolymer containing a pigment - wetting filler group to the alkynediol ethylene oxide adduct is preferably 3 - 5:1, more preferably 4:1; by utilizing the excellent steric hindrance effect of the polymer - type super - dispersant and the extremely low dynamic surface tension of the alkynol ethylene oxide adduct, the grinding efficiency can be effectively improved, and at the same time, the defect of particle agglomeration caused by the possible competitive adsorption of ionic dispersants during the drying process can be avoided.

[0056] In the present invention, the mass of the second grinding aid is preferably 0.5 - 1‰ of the mass of the marble coarse powder, more preferably 0.8 - 1‰.

[0057] In the present invention, the second wet grinding is preferably carried out in a second vertical stirring mill. The specification of the second vertical stirring mill is preferably 3600L. The grinding medium is preferably zirconia beads. The filling rate of the zirconia beads in the second vertical stirring mill is preferably 70-80%, more preferably 75%. The size of the grinding medium preferably includes 0.4mm, 0.6mm and 0.8mm. The mass ratio of the 0.4mm, 0.6mm and 0.8mm zirconia beads is preferably 2-4:1-2:1, more preferably 3-4:1-2:1.

[0058] In the present invention, the second grinding aid is preferably divided into a first part of the second grinding aid and a second part of the second grinding aid. The mixing of the first slurry and the second grinding aid preferably includes pumping the first slurry into a first slurry storage tank, adding the first part of the second grinding aid, and performing a second stirring. Then, pumping the obtained second stirred slurry into the second vertical stirring mill. The second part of the second grinding aid is preferably added through the top of the second vertical stirring mill. In the present invention, the second grinding aid is added in two portions to make more full use of the dispersant. There is no proportional limitation on the mass of the second grinding aid added twice in the present invention. In the examples, the mass ratio of the first part of the second grinding aid to the second part of the second grinding aid is preferably 1:1.

[0059] In the present invention, the time of the second wet grinding is preferably 30-40 min, more preferably 35-40 min.

[0060] In the present invention, the second slurry is preferably subjected to wet classification treatment by a wet classification system, and the classified slurry enters a second slurry storage tank.

[0061] In the present invention, the wet classification system is a horizontal spiral centrifugal classifier; the rotational speed difference of the differential of the horizontal spiral centrifugal classifier is preferably 10 r / min. By using the centrifugal acceleration generated by the high-speed rotation of the spiral, which is much higher than the gravitational acceleration, the sedimentation speed of the particles in the slurry is significantly increased to perform ultra-fine classification. Compared with the traditional wet grinding process without wet classification, it effectively avoids a small part of large particle materials that may exist in the slurry, thereby obtaining a slurry with a narrow particle size distribution.

[0062] In the present invention, the D of the material in the classified slurry 50 is preferably 0.6-0.7 μm, more preferably 0.61-0.68 μm, and even more preferably 0.64 μm; D 97 is preferably 1.2-1.3 μm, more preferably 1.22-1.28 μm, and even more preferably 1.25 μm; D 100 is preferably 1.5-1.6 μm, more preferably 1.51-1.58 μm, and even more preferably 1.54 μm.

[0063] Preferably, the classified slurry is pumped into a rotary flash drying system for flash drying, and after drying, it is collected by a cyclone and enters the finished product bin, and then sieved to obtain wet ground calcium carbonate.

[0064] In the present invention, the heat source for the flash drying is natural gas, which can effectively avoid the defect that when coal is used as the heat source in the traditional method, impurities may exist in the hot air, resulting in the appearance of black spots in the finally dried finished product.

[0065] In the present invention, the temperature of the heat source during the flash drying is preferably 380 - 400 °C, more preferably 390 - 400 °C, the temperature of the air outlet is preferably 200 - 220 °C, more preferably 210 - 220 °C, and the current of the blower is preferably 180 - 190 A, more preferably 185 - 190 A.

[0066] The present invention provides wet ground calcium carbonate prepared by the above preparation method.

[0067] In the present invention, the D of the wet ground calcium carbonate 50 is preferably 0.6 - 0.7 μm, more preferably 0.62 - 0.63 μm, and the D 97 is preferably 1.2 - 1.3 μm, more preferably 1.23 - 1.27 μm, and the D 100 is preferably 1.5 - 1.6 μm, more preferably 1.51 - 1.58 μm, and even more preferably 1.54 μm.

[0068] The present invention provides the application of the above wet ground calcium carbonate in the coating field.

[0069] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0070] The ring-roll mill models used in Examples 1 - 3 of the present invention are YFM-208;

[0071] The specifications of the first vertical stirrer mill and the second vertical stirrer mill used are 3600 L;

[0072] The LμmitenN-OC 30 used is purchased from BASF;

[0073] The PEG-1000 used is purchased from Nantong Yixun Biotechnology Co., Ltd.;

[0074] The SN-1798 and SN-3740 used are both purchased from Shanghai Shenzhu Chemical Technology Co., Ltd.;

[0075] The heat source of the rotary flash drying system used is natural gas.

[0076] Example 1

[0077] As Figure 1 shown, marble ore with a calcium carbonate content of ≥90 wt% is washed, dried, and subjected to jaw crushing and hammer crushing to obtain marble particles with a diameter of 10 - 50 mm;

[0078] The marble particles are conveyed by a spiral auger into a ring-roll mill for grinding to obtain marble coarse powder with D 50 = 8.07 μm and D 97 = 30.26 μm. The obtained marble coarse powder is mixed with water to prepare a marble slurry with a solid content of 40 wt%;

[0079] After stirring the marble slurry for 5 min, it is mixed with the first part of the first grinding aid (LμmitenN-OC 30 and PEG-1000 with a mass ratio of 1:2) accounting for 0.5‰ of the mass of the marble coarse powder, and subjected to the first stirring for 10 min. The obtained first stirred slurry is pumped into a first vertical stirring mill for the first wet grinding. The filling rate of zirconia beads in the first vertical stirring mill is 60%, and the mass ratio of 1.0 mm and 1.8 mm zirconia beads is 2:1. The second part of the first grinding aid (LμmitenN-OC 30 and PEG-1000 with a mass ratio of 1:2) accounting for 0.5‰ of the mass of the marble coarse powder is added to the top of the first vertical stirring mill, and grinding is carried out for 30 min to obtain the first slurry. Tested by a Malvern 3000-E laser particle size analyzer, the D 50 = 1.67 μm and D 97 = 3.37 μm of the materials in the obtained first slurry, and the mass proportion of the materials with a particle size ≤2 μm in the first slurry is 66.2%;

[0080] The first slurry is pumped into a first slurry storage tank, and the first part of the second grinding aid (SN-1798 and SN-3740 with a mass ratio of 3:1) accounting for 0.5‰ of the mass of the marble coarse powder is added, and the second stirring is carried out for 10 min. The obtained second stirred slurry is pumped into a second vertical stirring mill for the second wet grinding. The filling rate of zirconia beads in the second vertical stirring mill is 70%, and the mass ratio of 0.4 mm, 0.6 mm, and 0.8 mm zirconia beads is 2:1:1. The second grinding aid (SN-1798 and SN-3740 with a mass ratio of 3:1) accounting for 0.5‰ of the mass of the marble coarse powder is added to the top of the second vertical stirring mill, and the grinding time is 30 min to obtain the second slurry;

[0081] The second slurry is subjected to wet classification treatment through a wet classification system. The rotational speed difference of the differential of the horizontal screw centrifugal classifier is 10 r / min. The obtained classified slurry enters the second slurry storage tank and is tested by a Malvern 3000-E laser particle size analyzer. In the classified slurry, the D 50 = 0.68 μm, D 97 = 1.28 μm, D 100 = 1.58 μm;

[0082] The classified slurry is pumped into a rotary flash drying system for drying. The heat source temperature is 380 °C, the outlet temperature is 200 °C, the current of the blower is 180 A. After cyclone collection, it enters the finished product bin and is sieved to obtain wet ground calcium carbonate. Its D 50 = 0.70 μm, D 97 = 1.30 μm, D 100 = 1.58 μm.

[0083] Example 2

[0084] Marble ore with calcium carbonate content ≥ 90 wt% is cleaned, dried, subjected to jaw crushing and hammer crushing to obtain marble particles with a diameter of 10 - 50 mm;

[0085] The marble particles are transported by a spiral auger into a ring roll mill for grinding to obtain marble coarse powder with D 50 = 7.98 μm, D 97 = 29.78 μm. The obtained marble coarse powder is mixed with water to prepare a marble slurry with a solid content of 45 wt%;

[0086] After the marble slurry is stirred for 8 min, it is mixed with the first part of the first grinding aid with a mass of 0.8‰ of the mass of the marble coarse powder (LμmitenN-OC 30 and PEG-1000 with a mass ratio of 1:3) for the first stirring for 10 min. The obtained first stirred slurry is pumped into a first vertical stirring mill for the first wet grinding. The filling rate of zirconia beads in the first vertical stirring mill is 65%, and the mass ratio of 1.0 mm and 1.8 mm zirconia beads is 3:1. The second part of the first grinding aid with a mass of 0.8‰ of the mass of the marble coarse powder (LμmitenN-OC 30 and PEG-1000 with a mass ratio of 1:3) is added to the top of the first vertical stirring mill and ground for 35 min to obtain the first slurry. Tested by a Malvern 3000-E laser particle size analyzer, the D 50 = 1.62 μm, D 97 = 3.31 μm, and the mass ratio of the material particle size ≤ 2 μm in the first slurry is 68.5%;

[0087] Pump the first slurry into the first slurry storage tank, add the first part of the second grinding aid (SN-1798 and SN-3740 with a mass ratio of 4:1) accounting for 0.8‰ of the mass of the coarse marble powder, conduct the second stirring for 10 minutes. The obtained second stirred slurry is pumped into the second vertical stirring mill for the second wet grinding. The filling rate of zirconia beads in the second vertical stirring mill is 75%, and the mass ratio of 0.4mm, 0.6mm, and 0.8mm zirconia beads is 3:2:1. Add the second grinding aid (SN-1798 and SN-3740 with a mass ratio of 4:1) accounting for 0.8‰ of the mass of the coarse marble powder at the top of the second vertical stirring mill, and grind for 35 minutes to obtain the second slurry;

[0088] Conduct wet classification treatment on the second slurry through a wet classification system. The rotational speed difference of the differential of the horizontal screw centrifugal classifier is 10 r / min. The obtained classified slurry enters the second slurry storage tank and is tested by a Malvern 3000-E laser particle size analyzer. In the classified slurry, the D 50 = 0.64μm, D 97 = 1.25μm, D 100 = 1.54μm;

[0089] Pump the classified slurry into a rotary flash drying system for drying. The heat source temperature is 390°C, the outlet temperature is 210°C, the current of the blower is 185 A. After cyclone collection, it enters the finished product bin and is sieved to obtain wet ground calcium carbonate, with D 50 = 0.63μm, D 97 = 1.27μm, D 100 = 1.54μm.

[0090] Example 3

[0091] After washing, drying, jaw crushing, and hammer crushing of the marble raw ore with a calcium carbonate content ≥ 90 wt%, marble particles with a diameter of 10 - 50 mm are obtained;

[0092] Transport the marble particles into a ring roll mill through a spiral auger for grinding to obtain marble coarse powder with D 50 = 7.99μm and D 97 = 29.87μm. Mix the obtained marble coarse powder with water to prepare a marble slurry with a solid content of 50 wt%;

[0093] After stirring the marble slurry for 10 min, mix it with the first part of the first grinding aid, which is 1‰ of the mass of the coarse marble powder (Lμmiten N-OC 30 and PEG-1000 with a mass ratio of 1:4), and conduct the first stirring for 10 min. Pump the obtained first stirred slurry into the first vertical stirring mill for the first wet grinding. The filling rate of zirconia beads in the first vertical stirring mill is 70%, and the mass ratio of 1.0 mm and 1.8 mm zirconia beads is 4:1. Add the second part of the first grinding aid, which is 1‰ of the mass of the coarse marble powder (Lμmiten N-OC 30 and PEG-1000 with a mass ratio of 1:4), to the top of the first vertical stirring mill and grind for 40 min to obtain the first slurry. After testing with a Malvern 3000-E laser particle size analyzer, the D 50 of the material in the obtained first slurry is 1.55 μm, and D 97 is 3.26 μm. The mass proportion of the material with a particle size ≤ 2 μm in the first slurry is 70.6%;

[0094] Pump the first slurry into the first slurry storage tank, add the first part of the second grinding aid, which is 1‰ of the mass of the coarse marble powder (SN-1798 and SN-3740 with a mass ratio of 5:1), and conduct secondary stirring for 10 min. Pump the obtained second stirred slurry into the second vertical stirring mill for the second wet grinding. The filling rate of zirconia beads in the second vertical stirring mill is 80%, and the mass ratio of 0.4 mm, 0.6 mm, and 0.8 mm zirconia beads is 4:1:1. Add the second grinding aid, which is 1‰ of the mass of the coarse marble powder (SN-1798 and SN-3740 with a mass ratio of 5:1), to the top of the second vertical stirring mill and grind for 40 min to obtain the second slurry;

[0095] Conduct wet classification treatment on the second slurry through a wet classification system. The rotational speed difference of the differential of the horizontal screw centrifugal classifier is 10 r / min. Let the obtained classified slurry enter the second slurry storage tank. After testing with a Malvern 3000-E laser particle size analyzer, the D 50 of the material in the classified slurry is 0.61 μm, D 97 is 1.22 μm, D 100 is 1.51 μm to obtain the classified slurry;

[0096] Pump the classified slurry into a rotary flash drying system for drying. The heat source temperature is 400 °C, the outlet air temperature is 220 °C, the current of the blower is 190 A. After cyclone collection, it enters the finished product bin and is sieved to obtain wet ground calcium carbonate, with its D 50 being 0.62 μm, D 97 being 1.23 μm, D 100 being 1.51 μm.

[0097] Comparative Example 1

[0098] Heavy calcium carbonate produced by traditional wet grinding process, specifically, nano calcium carbonate from Jiangxi Guangyuan Chemical Co., Ltd. was selected.

[0099] Performance Test

[0100] 1. According to HG / T 3249-2013, the index tests were carried out on the wet heavy calcium carbonate of Examples 1 to 3 and Comparative Example 1, and the results are shown in Table 1.

[0101] Table 1 Index test results of wet heavy calcium carbonate of Examples 1 to 3 and Comparative Example 1

[0102]

[0103] As can be seen from Table 1, compared with Comparative Example 1, when the slurry particle sizes of Examples 1 to 3 were basically the same, the particle sizes of the dry powders (i.e., the obtained wet heavy calcium carbonate products) of Examples 1 to 3 were basically the same as those of the materials in the slurry (i.e., the obtained classified slurry), while the particle sizes of the dry powder of traditional wet heavy calcium carbonate were significantly inconsistent with those of the materials in the slurry, with obvious particle agglomeration. Moreover, the specific surface area of the dry powders of Examples 1 to 3 was significantly better than that of traditional wet heavy calcium carbonate, indicating that the wet heavy calcium carbonate produced by the method of the present invention can effectively avoid the problem of powder agglomeration during drying, and make the dry powder present the original particle size of the materials in the slurry in the slurry state.

[0104] 2. The wet heavy calcium carbonate of Examples 1 to 3 and Comparative Example 1 was made into interior wall latex paint according to the formula in Table 2, and the contrast ratio, wet hiding power, viscosity and scrub resistance were detected by the following methods. After storing at 50 °C for 7 days, the heat storage performance was observed, and the results are shown in Table 3;

[0105] Contrast ratio: GB / T23981.1-2019;

[0106] Wet hiding power: BGD 298;

[0107] Viscosity: GB / T 9269—2009;

[0108] Scrub resistance: GB / T9266-2009.

[0109] Table 2 Interior wall latex paint formula

[0110]

[0111] Table 3 Performance test results of interior wall latex paint made from wet heavy calcium carbonate of Examples 1 to 3 and Comparative Example 1

[0112] Item 1# 2# 3# 4# Contrast Ratio / % 0.9289 0.9296 0.9302 0.9124 Wet Hiding Power / μm 32 31 30 40 Viscosity / KU 103.3 103.4 103.4 106.4 Heat Storage at 50°C for 7 Days No Water Separation No Water Separation No Water Separation Slight Water Separation Scrub Resistance / times 594 589 590 562

[0113] As can be seen from Table 3, when Examples 1 to 3 produced by the method of the present invention are used to prepare interior wall latex paint, compared with traditional wet ground calcium carbonate, the hiding performance is significantly improved (both the contrast ratio and wet hiding are significantly improved), and the storage stability is also significantly better than that of traditional wet ground calcium carbonate (no water separation after heat storage at 50°C for 7 days), and the performance is significantly improved.

[0114] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of wet ground calcium carbonate, characterized in that, It includes the following steps: Grind marble particles, mix the obtained coarse marble powder with water to obtain a marble slurry; Mix the marble slurry with a first grinding aid and perform first wet grinding to obtain a first slurry; Mix the first slurry with a second grinding aid and perform second wet grinding to obtain a second slurry; Perform wet classification on the second slurry to obtain a classified slurry; Perform flash drying on the classified slurry to obtain wet ground calcium carbonate; The first grinding aid includes a non-ionic fatty alcohol ethoxylate and polyethylene glycol; The second grinding aid includes a high molecular weight block copolymer containing a pigment-affinity filler group and an alkynediol ethylene oxide adduct.

2. The preparation method according to claim 1, characterized in that, The marble particles are obtained by washing and coarsely crushing marble ore with a calcium carbonate content of ≥90 wt%, and the diameter of the marble particles is 10 - 50 nm.

3. The preparation method according to claim 1, characterized in that The particle size of the coarse marble powder is 325 - 400 mesh; the solid content of the marble slurry is 40 - 50 wt%.

4. The preparation method according to claim 1, characterized in that, The mass of the first grinding aid is 0.5 - 1‰ of the mass of the coarse marble powder, and the time of the first wet grinding is 30 - 40 min; The first wet grinding is carried out in a first vertical stirring mill. The first grinding aid is divided into a first part of the first grinding aid and a second part of the first grinding aid. The first part of the first grinding aid is mixed with the marble slurry, and the second part of the first grinding aid is added through the top of the first vertical stirring mill; The D of the material in the first slurry 50 =1.5~1.7μm, D 97 =3.2-3.4 μm, and the mass proportion of the material particle size ≤2 μm in the first slurry is >65%.

5. The preparation method according to claim 1, characterized in that, The mass of the second grinding aid is 0.5 - 1‰ of the mass of the coarse marble powder, and the time of the second wet grinding is 30 - 40 min; The second wet grinding is carried out in a second vertical stirring mill. The second grinding aid is divided into a first part of the second grinding aid and a second part of the second grinding aid. The first part of the second grinding aid is mixed with the first slurry, and the second part of the second grinding aid is added through the top of the second vertical stirring mill.

6. The preparation method according to claim 1, wherein, The D of the materials in the classified slurry 50 = 0.6 - 0.7 μm, for D 97 = 1.2 - 1.3 μm, for D 100 = 1.5 - 1.6 μm.

7. The preparation method according to claim 1, wherein, The heat source for the flash drying is natural gas. When flash drying, the heat source temperature is 380 - 400 °C, the outlet temperature is 200 - 220 °C, and the current of the blower is 180 - 190 A.

8. The preparation method according to claim 1, characterized in that The non-ionic fatty alcohol ethoxylate includes LμmitenN-OC 30, the average molecular weight of the polyethylene glycol is 1000, and the mass ratio of the non-ionic fatty alcohol ethoxylate to the polyethylene glycol is 1:2 - 4; The high molecular weight block copolymer containing a pigment-affinity filler group includes SN-1798, the alkynediol ethylene oxide adduct includes SN-3740, and the mass ratio of the high molecular weight block copolymer containing a pigment-affinity filler group to the alkynediol ethylene oxide adduct is 3 - 5:

1.

9. The wet ground calcium carbonate prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The D of the wet ground calcium carbonate 50 = 0.6 - 0.7 μm, D 97 = 1.2 - 1.3 μm, D 100 = 1.5 - 1.6 μm.

10. Application of the wet ground calcium carbonate according to claim 9 in the field of coatings.

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